Surface-hardened material and method for producing the same



Patented Nov. 26, 1929 UNITED'STATES PATENT OFFICE AUGUSTUS B. KINZEL, OF NEW YORK, N. 'Y., ASSIGNOR TO ELECTRO METALLURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA SURFACE-'HARDENED' MATERIAL AND METHOD FOR PRODUCING THE SAME No Drawing. Application filed July 28,

My invention relates to the surface hardenthe hardening being effected b the action of nitrogen-containing compoun s, for example ammonia.

The hardening effect produced by heating ferrous metal in contactwith ammonia and other nitrogenous compounds is known. It is also known that a desirable degree of hardness'can only be obtained by this method when the ferrous metal treated contains certain alloying elements, and when such alloying elements are present in critical amount. Acceptable hardening has been obtained When the alloying element used was alumi- 1111111. Aluminum is not a desirable alloying element in steel, as it tends to produce oxide inclusions and other defects which impair the quality of the steel, particularly with respect to fatigue-resistance. The lack of desirable properties in those aluminum steels in which a hard surface layer can be developed by nitrogenizing seriously limits the commercial usefulness of structures made therefrom.

My invention provides means for making a hard and strong nitride coating on ferrous metals without introducing into the metal an undesirable constituent that will impair its properties.

I have discovered when aluminum is incorporated in ferrous metals only at the surface of the material where it is to be utilized to produce the desired hard and strong ni trogenized structure that the undesirable effect of aluminum in the core is avoided.

I provide a steel with an aluminized surface layer containing a content of aluminum such that a hardened layer will result when the steel is nitrogenized. The steel may be aluminized in any desired manner, but I prefer to heat the steel in contact with aluminum powder under neutral or reducing conditions at a temperature of about 500 to 800 C. I have obtained satisfactory results when the steel was treated with aluminum for one-half to two hours at 550 (1, but other temperatures and times may be used. If, by chance the concentration of aluminum in the surface 1927. "serin no. 209,184.

becomes too great, I may reduce it'to the desired value by soaking the steel at a suitable temperature, as for e'xampleabout 900 C.

The surface-aluminized steel is then heated to about 500 to580 C. in the presence of a substance, such as ammonia, that yields nitrogen to the material. This treatment provides a hard nitrogenized compound of the kind described above only as a surface layer and the properties of the core of the material will not be detrimentally affected. Thenitrogenization' preferably is carried out at a" temperature not materially above 580 0., and under these conditions there is no serious embrittling of the interior portions of the member treated. Y

-My process is applicable to iron, steel and all ferrous alloys that are capable of absorbing a coating of aluminum, and may be applied to steel containing an amount of aluminum less than the critical amount necessary to produce the desired hard coating. For example, I place a low carbon steel containing 12% chromium in a closed furnace chamber in a mixture of aluminum and aluminum 7 oxide. The chamber and its contents are heated to a temperatureof about 500 0., in an atmosphere of hydrogen for about two hours and then the steel is transferred with or without cooling to another furnace and maintained in the latter furnace in an atmosphere of ammonia at 510 C. After treating in the latter furnace, the steel acquires a thin, hard, tough coating corresponding to about 900 of the Brinell scale. The hardness of a carbon steel containing 35% carbon when aluminized and treated in accordance with my invention was likewise increased to about 900 Brinell. For most practical urposes, a hardness greater than 700 Brlnell is "desired and a hardness of at least 900 Brinell is preferred. v

The treated article resulting from my process has a core or foundation consisting of steel or 'alloy steel and a thin homogeneous surfacing material comprising aluminum and nitrogen that provides a hard, strong coating. The core of the article contains either no aluminum or aluminum in a concentration so small that the core material is not detri- 100v mentally affected to the degree that it is when the c'orecontains aluminum throughout in an amount sufficient to produce the desired hard nitrogenized surface layer.

Although I have described certain specific modifications of my invention, other modifications may be made without departing from'the spirit thereof. Therefore, I desire to be limited only by the prior art and by the invention as-defined in the annexed claims.

I claim:

1. The method of hardening ferrous material which comprises enriching'the material in its surface layer with aluminum and then heating the material to about 510 C. in the presence of ammonia;

2. The method ,of hardening ferrous material which comprises heating the same in contact with aluminum at a temperature suliicient to provide a surface layer enriched with aluminum and then heating the material in the presence of a substance that yields nitrogen.

i 3. The method of hardening ferrous material which comprises heatingthe same in contact with .aluminum at a temperature sufficient to provide a surface layer comprising aluminum and then heating the material to a temperature not exceeding 580 C. in the presence of a substance that yields nitrogen, said temperature being suflicient to nitrogenize the ferrous material.

4. The method of hardeningferrous material which comprises heating the same in contact with aluminum at a temperature sufficient to provide an aluminized coating thereon and then heating the material to about 510 C. in the presence of ammonia.

5. The method of hardening ferrous materialswhich comprises heating the same with aluminum to about 550 C. so as to form-a surface layer enriched with aluminum and then subjecting the material to a temperature of about 510 C. if e presence of ammonia.

6? The method of ardening the surface of 3 a ferrous material-which comprises providing an aluminized coating-on the material, the aluminum in said coating being of such concentration that a hardstructure of complex nitrides will be'formed only in the surface material that has been aluminized and then treated to form a hard nitrogenized body.

8.; An article comprising a core of ferrous material and an aluminized surface layer of said ferrous materlal, said surface layer comprising a compound of-nitrogen.

9. An articl comprising a core of ferrous material and .a surface layer of aluminized core material, said surface layer being harder than said core and comprising a compound of nitrogen.

10. An having a hard surface layer containing aluminum and nitrogen, and a softer interior portion having a lower content of aluminum.

11. An article comprising a core containing a substantial amount of chromium, said 1 article having an aluminized nitrogenized surface layer harder than that corresponding to 7 O0 Brinell.

12. The method of hardening ferrous ma terial which comprises adjusting the content of aluminum only in the surface layer of the material so that a hard structure of nitrogen containing material will be formed in the layer by heating to predetermined temperatures in the presence of a substance that 1 will yield nitrogen'thereto, and then heating the material in the presence of nitrogenyielding material.

13.- The methodof hardening ferrous material which comprises adjusting the content of aluminum only in the surface layer of the material sothat a hard structure of'nitrogencontaining material will be formed by heat ing to temperatures not exceeding 580 C. in the presence of a substance that will yield nitrogen thereto, and then heating the ma-' terial tov said temperatures in the presence of nitrogen-yielding material.

14. An article composed of a ferrous alloy, the surface layer of said alloy containing nitrogen and aluminum, the aluminum being present in a critical amount which will produce a hard nitrogen-containing substance corresponding to at least 700 Brinell by heating to tem eratures of about 500 C. in the presence 0 ammonia, the core being free from aluminum in amounts which will produce said hard nitrogen-containing substance at said temperatures. In testimony whereof I affix my signature.

AUGUSTUS B. KINZEL.

Player when it is subjected to a substance that article composed of ferrousmetal 1 

